The present invention relates to intraocular lenses and more particularly to improved haptics and optics for intraocular lenses.
Intraocular lenses are employed as replacements for the crystalline lens after either extracapsular or intracapsular surgery for the removal of a cataract. Intraocular lenses are generally of two types, those that are placed in the anterior chamber, i.e., between the iris and the cornea, and those that are placed in the posterior chamber, i.e., behind the iris. Both types of lenses are conventionally employed with the choice between an anterior chamber and a posterior chamber lens being partly dictated by requirements of the patient and partly dictated by the preferences of the physician inserting the lens. A third type of lens, known as iris-fixated lenses because they are secured to the iris periphery, can be thought of as being within one of the two types above, in that their optic portion is in either the anterior or posterior chamber.
Intraocular lenses normally consist of an optic with at least one and preferably two or more haptics that extend generally radially from the optic and contain distal portions that normally seat in the scleral spur for an anterior chamber lens and either in the ciliary sulcus or within the lens capsule for a posterior chamber lens. The optic normally comprises a circular transparent optical lens. The haptic in most lenses is a flexible fiber or filament having a proximate end affixed to the lens and having a distal end extending radially away from the periphery of the lens to form a seating foot. Several haptic designs are currently in use, for example, a pair of C-shaped loops in which both ends of each loop are connected to the lens, and, for example, J-shaped loops in which only one end of the loop is affixed to the lens.
The optimum position for a posterior chamber lens is in the capsular bag. This is an extremely difficult maneuver for the surgeon to accomplish. When a posterior chamber lens is employed it must be placed through the small pupillary opening, and the final haptic position is hidden behind the iris and not visible to the surgeon. It is therefore highly desirable to keep the overall dimensions of the posterior chamber lens as small as possible during implantation, letting it expand when it is finally situated where the surgeon intends, usually in the capsular bag. A small device is easier to manipulate in the eye, reduces the chance of the haptics coming in contact with the corneal endothelial tissue, and allows the surgeon ease of insertion, as he must often insert a lens with a 14 mm overall dimension through a pupil of 5 to 8 mm diameter. A smaller lens also reduces the lens/iris contact and can better guarantee that the intraocular lens and its haptics will be in the capsular bag. U.S. Pat. No. 4,527,294, discloses a lens having haptics that are capable of being compressed toward the lens body and detachably held thereon. This, however, would require a complicated maneuver for the surgeon and a two-handed insertion technique. Other proposals have sought to attach the distal end of the haptic to the periphery of the optic; this attachment would then be released mechanically by the surgeon after implantation. Unfortunately, the surgeon would have the problem of the uncertainty of finding and releasing the mechanism when the lens periphery is hidden behind the iris after implantation. It would therefore be desirable to have a posterior chamber intraocular lens in which haptics would remain closed until placed behind the iris and would then open automatically without further instrument intervention. This could guarantee successful capsular bag implantation.
As mentioned earlier, intraocular lenses are characterized by a lens body and a plurality of flexible haptics which are usually radially resilient and that extend outwardly from the periphery of the lens and which gently, but elastically, engage appropriate circumferential eye structure adjacent the iris or within the capsular bag. This resiliency is due to the elastic properties of the materials of the haptic. The result is a haptic which when compressed and released will uncontrollably spring back immediately. This property makes the process of implantation and final positioning of the lens difficult since the haptics must be constrained during implantation. U.S. Pat. No. 4,527,294 discloses haptics having a manipulator attached thereto to control the springback until the elns is in final position. U.S. Pat. No. 4,426,741 discloses a closed-loop haptic having a pivotal haptic/optic connection to mitigate the uncontrollable springback of the haptic material. It would be very desirable to have a lens having a mechanical memory whereby the device could be deformed from its free shape to a compact shape which it would maintain for easy implantation and that would restore itself to its free shape in situ without the complex manipulations required in U.S. Pat. No. 4,527,294 mentioned earlier.
Also, once situated, the flexibility of the conventional haptic material makes the lens susceptible to decentration from being pushed by vitreous pressure from behind the lens or shifting due to pressure from adjacent ocular tissue. It would be desirable for centration purposes to have a lens which is flexible where it contacts ocular tissue and which is relatively rigid at the haptic/optic junction.
In recent years intraocular lenses with and without haptics having relatively soft body portions have been provided such that the body portion could be folded generally across the diameter thereof for insertion into a smaller opening during implantation of the lens. U.S. Pat. No. 4,466,705 to Michelson, which is incorporated herein by reference, discloses a fluid sheath having liquid therein. The use of a liquid or hydrogel allows the lens body to be folded before insertion and then subsequently filled when in position. Unfortunately, the soft materials used for the bodies of these lenses lack the restorative strength sometimes required to return to their original shape. It would be highly desirable to have a lens of such soft material not necessarily having haptics but having a component having a mechanical memory associated with the lens body that would restore the soft lens to its original shape and would also provide dimensional stability to the lens in its final position in the eye.
In the past shape memory alloys have been proposed for use in the medical field. For example, U.S. Pat. No. 3,620,212 proposes the use of such an alloy in an intrauterine contraceptive device, U.S. Pat. No. 3,786,806 proposes the use of such alloy in a bone plate, and U.S. Pat. No. 3,890,977 proposes the use of such an alloy to bend a catheter or cannula. The foregoing patents rely on the temperature-transition property of shape memory alloy. In addition, European Patent Application No. 0 145 166, published June 19, 1985, discloses the use of shape memory alloys exhibiting pseudoelasticity and which display stress-induced martensite in the above medical devices. None of those disclosures, however, suggest the use of any shape memory alloy as an integral part of a device to be permanently implanted within the extremely sensitive and close confines of the human eye. Specifically, none of those disclosures contemplate the use of shape memory alloy as an active and precise positioning mechanism. None of those disclosures realize the importance of not only being able to insert an intraocular lens through several minute openings (an incision, pupilary opening and the anterior opening of the capsular bag) during microsurgery, but also to have the lens situate itself in a precise location, and fixate that position with calculable dimensional stability. By comparison, the devices described in the prior art would appear crude and non-analogous. It would therefore be most desirable to have an intraocular lens that would utilize extraordinary properties of shape memory alloy for precise movement and positioning of a lens within the human eye.